Poor Top End Power and Throttle Response, High "sticky" Idle

[yukongt94]

I just purchased my first bike, a 2004 250 with 2600 miles on it. The day I test rode the bike, it was around 60 degrees outside, and it ran great. Great throttle response and lots of power especially up top. Since that day, the outside temperatures have been lower (45 or less), and the bike is running poorly. I'm not sure the temperatures have anything to do with it, just mentioning.

I filled the tank with 3 gallons of fresh 87 and half a bottle of Gumout Regane Fuel Cleaner. I have ridden the bike two times since purchase, and have done about 20 miles - it's condition is not getting any better.

The bike always starts up right away when cold using 75% or a bit more of choke. The rpms start around 3000, and I then push a bit of choke out to bring them back down towards 1400. However, once the bike is warmed up when I come to a stop the idle will hang around 3500 rpm. I can manually make it come down by slipping the clutch, and then it will hang closer to 1500. However anytime I come to a stop without doing that, it will hang at the 3500 mark. Whichever rpm it's idling at, it is smooth and does not surge.

Additionally, there is a large amount of hesitation in the throttle when the bike is cold. I've tried different levels of choke, and the hesitation is still there until the bike warms up. What I mean by this is if I give it any more than say 30% throttle when it's cold and choked, the engine won't rev up and will stall. However if I give it just a little throttle to get the rpms up, I can then rev the bike freely.

Even after I had the choke off and the bike is warmed up all the way, the throttle response is still quite low, and did not seem to like to rev up much past 9000. When riding, there was decent mid range power, but it did not have anywhere near the top end power it should. Even wide open the acceleration was very very slow. The sound the engine is making doesn't seem quite right either. Almost like a very minor stumbling, and I did hear some minor backfiring once or twice around 6000rpm.

Any help would be greatly appreciated. Thanks and Happy Riding!

[bob706]

Welcome to the forum Have you tried adjusting the idle?

[yukongt94]

I have yet to bother with the idle adjustment screw, as the bike does seem to idle correctly until it's revved up or brought to a stop. Is there suppose to be an adjustment from hot and cold? I can let the bike warm up for a few minutes and it stays around 1400 just fine, but after it's warm and I come to a stop is when it seems to hang around 3500, very similar to what it does when I've got too much choke in it. Very confused as to why ti can idle fine some of the time and then way off at others...

[yukongt94]

Could the fuel system cleaner cause this power problem if I put too much in? Maybe half a bottle was too much for 4 gallons or so.... just seems like it started running this way after that. Although I do remember the idle hanging before the cleaner, it was running excellent before. Or maybe I'm way off base hoping for an easy fix.
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[yukongt94]

I drained all the fuel and filled the bike back up with 3 gallons of fresh 87. After 15 more miles the bike is still running just as badly. It's so low on power, I'd say 0-30 takes more than ten seconds.

Is there any chance it's something more simple like fouled plugs? The more I think about it, it seems (and sounds) like the bike is running with either too much or too little fuel. The tone of the engine is totally different anywhere above 6000 rpm than it was when running properly. It doesn't sound like some kind of internal engine parts problem, more like it's struggling or wheezing for fuel/air/spark. It's acting almost like the choke is still on, even when all the way off.

I'm starting to get worried if I'll ever be able to figure this thing out. I want it to run well so badly, and when it's acting this way it concerns me. Then I keep seeing those Honda commercials that go "I wanna ride I wanna ride I wanna ride" and it adds insult to injury...

[yukongt94]

Also, I did adjust the idle screw when the rpms were hanging around 3500. After they came down to where they should be, I shut the bike off. Then I realized that now the idle was set too low to stay running. I readjusted it to where it was before, and it still occassionally hangs at 3500 when coming to a stop, but always starts up and idles perfectly at 1400 once warm.

[kkim]

sounds like you might have a slight vacuum leak. try checking the carb clamps on the engine and airbox side of the carbs. also, check any vacuum hoses to see if they are loose, damaged or disconnected.

when was the last time the valves were checked?

[yukongt94]

Ah the vacuum lines I'll give those a thorough once over, certainly didn't think of those thanks.

I haven't checked the valves at all, not sure I trust myself enough to touch them unfortunately

[FrugalNinja250]

A seven year old bike with only 2,600 miles on it, I'm pretty much betting the carbs need to be removed, fully dismantled, and cleaned. It's not hard to do, just tedious. You'll need a good spray solvent (I highly recommend Brakleen, red can not green can) and compressed air, as well as some small bristle brushes and a decent set of hand tools. While you're in there you can go ahead and add a real fuel filter.

[kkim]

Andrew,

Sorry, with such low mileage, I doubt the valves are the problem. If you check the vacuum hoses and they all look okay, as frugal mentioned, your next step would be to inspect/clean the carbs.

[speedgsx98]

Sounds like a jetting issue. You definitely need to adjust your idle. It's not a screw, but a little black dial on the left side of the bike just at the base of the carbs. Maybe someone fooked with the jetting prior to you buying your bike. I know that when my engine is cold when I leave work at night...it takes noticeably longer to accelerate and requires much more throttle until it is warmed up.

Best of luck and keep us informed on your progress.

[yukongt94]

Thanks for the help so far folks, really appreciate the support of this board... anyway, I think I may I have caught a lucky break today after I went for a more extended (30 miles). I really tried revving the engine out even though it didn't like to rev freely up top. However it seems to have done the trick, all of a sudden the bike stumbled a bit and all the power came back. This thing is a rocketship in comparison now haha.

The idle seems to have improved as well in conjunction after I adjusted the black knob once it was fully warmed up. It still sticks occasionally but for the most part is right around 1500. I'm not sure any of this has bearing on the improvements, but I did a rotella t6 oil change today. Also, I switched the petcock to reserve before the ride. The power didn't come back until 20 or so miles into the ride.

In any case, the smile on my face was hard to get rid of once it started running well again. Hopefully it continues to run this well in the future. I will update the thread again tomorrow after another ride.
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[kkim]

if you think it was a fuel problem, try running some Seafoam in your gas for a couple of tanks and see if it helps.